Biogeographical and cross-shelf patterns of reef fish assemblages in a transition zone

Transition zones have complex patterns of biogeography and biodiversity which require consideration in conservation planning. Cross-shelf patterns of reef fish assemblage structure and biogeographic representation were determined for the Solitary Islands Marine Park (SIMP), positioned in a tropical-temperate overlap on the east coast of Australia. Sixty-eight sites were surveyed on shallow (\u3c25 m) reefs across an inshore–offshore gradient, using timed counts. Tropical taxa were most prevalent, comprising 50% of the 254 species recorded. Australian endemics accounted for 23% of species, with east coast endemics (14%) predominating. There was a strong cross-shelf gradient, with species richness increasing offshore. There was also a distinct biogeographical gradient with the proportion of temperate species decreasing and tropical species increasing with increasing distance from shore. This gradient was similar for endemic and cosmopolitan species as many of the endemics were temperate or subtropical, and many of the tropical species were widespread Indo-Pacific taxa. These patterns are consistent with sites further offshore being more frequently exposed to the tropical East Australian Current (EAC). Patterns on reefs further inshore are consistent with the high levels of endemism previously reported for temperate and subtropical Australian waters. The complex cross-shelf arrangement of tropical, subtropical and temperate species results in high regional biodiversity and needs to be recognised in marine-park planning

The application of predicted habitat models to investigate the spatial ecology of demersal fish assemblages

Benthic habitats are known to influence the abundance and richness of demersal fish assemblages; however, little is known about how habitat structure and composition influences these distributions at very fine scales. We examined how the benthic environment structures marine fish assemblages using high-resolution bathymetry and accurate predicted benthic habitat maps. Areas characterised by a mosaic of habitat patches supported the highest richness of demersal fishes. A total of 37.4% of the variation in the distribution of the fish assemblage was attributed to 6 significant variables. Depth explained 23.0% of the variation, with the boulders explaining 12.6% and relief 1.4%. The remaining measures (seawhips, light/exposure and solid reef) provided a small (<1.0%) but significant contribution. Identifying components of the benthic environment important in structuring fish assemblages and understanding how they influence the spatial distribution of marine fishes is imperative for better management of demersal fish population